meihuak what did you attempt and what happened?
Link labels should support any UTF-8 character.
Links might have a validation rule that maybe prevents some UTF-8 characters (?) You should be able to urlencode them before pasting the URL if necessary. You might need to write domain name in punnycode.
EDIT: I now see the title of the merged discussion. If you mean having multiple labels that switch when the language is switched, that's not supported.
However translating link labels and URLs is a feature offered by this paid extension (not created by FriendsOfFlarum) https://discuss.flarum.org/d/30487-localizd-truly-multi-lingual